EFFECTIVENESS OF LOTUS ROOT-NODULES .1. MORPHOLOGY AND FLAVOLAN CONTENT OF NODULES FORMED ON LOTUS-PEDUNCULATUS BY FAST-GROWING LOTUS RHIZOBIA

The morphology of root nodules formed on Lotus pedunculatus by two fast-growing strains of Rhizobium, NZP2037 which forms effective (nitrogen-fixing) nodules and NZP2213 which forms ineffective (non-nitrogen-fixing) nodules, has been studied. The nodules formed by NZP2037 contained a central zone of bacteroid-filled plant cells surrounded by a cortex. In contrast the nodules formed by NZP2213 contained no Rhizoblum-infected plant cells, but rhizobia were found in localized areas on the nodule surface and between the outer two or three cell layers of the nodule. Electron-dense osmiophilic deposits identified as flavolans (condensed tannins) were present in the vacuoles of many uninfected plant cells in the nodules formed by both Rhizobium strains. This is the first time that flavolans have been positively identified in legume root nodules. In the NZP2037 nodule flavolans were present in the outer cortical and epidermal cells. In the ineffecitve NZP2213 nodule fiavolans were present in many of the central nodule cells. The concentration of flavolan in the NZP2213 nodule was 12 times higher than in the NZP2037 nodule. © 1979 Oxford University Press.